Liquid-absorbent sheet and method for storing food using the same

ABSTRACT

A liquid-absorbent sheet containing a liquid-absorbing material capable of absorbing drips of food, wherein a part of the outer surface of the liquid-absorbent sheet is composed of a liquid-permeable film, a part of other outer surface thereof is composed of a liquid-semipermeable film, the liquid-semipermeable film is a liquid-impermeable film having formed therein pores, the diameter of the pore is in the range of from 0.05 mm to 0.5 mm, and the porosity of the pores is in the range of from 0.01% to 0.4%. The liquid-absorbent sheet effectively absorbs drips oozing from a drippy food to prevent deterioration in qualities of the food for a prolonged period of time.

This is a divisional of application Ser. No. 08/385,131 filed Feb. 7,1995, abandoned.

FIELD OF THE INVENTION

The present invention relates to a liquid-absorbent sheet capable ofabsorbing off drips oozing from the surfaces of a drippy food such asmeat and fish, and capable of preventing deterioration in qualities ofthe food for a long period of time without drying the food by positivelynot absorbing water in the food, and also to a method for storing a foodusing the liquid-absorbent sheet.

BACKGROUND OF THE INVENTION

When a food such as meat or fish is vacuum-packaged in a gas-impermeablebag and stored at a chilled temperature or stored in a frozen state andthen thawed, a liquid called "drips" oozes from the food. These dripsare pooled in a space between the food and the gas-impermeable bag. Whenthe food comes in contact with these drips, it undergoes deterioration(for example, discoloration) in the qualities and thus its commercialvalue is seriously reduced. On the other hand, the elimination of thediscolored part lowers the yield of the food. Furthermore, the dripssuit for the growth of bacteria, resulting in a shortened shelf life ofthe food.

Therefore, attempts-have been made to develop a method for eliminatingthe drips from a food. The method generally comprises packaging a foodwhile being in contact with a liquid-absorbent material in the form of asheet which absorbs drips oozing from the food during storage. Theliquid-absorbent materials that have been employed for the purpose arecapillary liquid-absorbent materials such as paper pulp having ahydrophilic surface and capable of absorbing and retaining drips via thecapillary action; so-called polymeric water absorbents; and compositematerials consisting thereof. However, these capillary liquid-absorbentmaterials are poor in strength as a sheet material. The polymeric waterabsorbents are generally in the form of a powder or granules and aretroublesome when they are brought into contact with a food. Accordingly,these liquid-absorbent materials are covered with a liquid-permeablefilm such as a nonwoven fabric and used as a liquid-absorbent sheet, asdescribed in JP-B-1-12539 and JP-B-6-53226. (the term "JP-B" as usedherein means an "examined Japanese patent publication")

The liquid-absorbent sheet covers a large part of food surface or isplaced under the bottom surface of food in the case of vacuum packagingthe food with a gas-impermeable film, being chilled and transported.This is because even the food is vacuum packaged with a gas-impermeablesheet, the drip oozing from the food due to gravity and shake duringtransporting stays at bottom portions of the packages and hollowportions of the food. By placing the liquid-absorbent sheet at theabove-mentioned positions so that the drip is absorbed in theliquid-absorbent sheet, which is the most important purpose of theliquid-absorbent sheet, the food can be kept away from the drip.

However, when a part of the outer surface of the liquid-absorbent sheetis composed of a liquid-permeable film and the liquid-permeable film iscontacted with the food, the liquid-absorbent sheet positively absorbsnot only the drip staying in the space between the food and thegas-impermeable film but also water in the food at the surface thereofin contact with the liquid-absorbent sheet and as a result the food isdried and the quality is deteriorated.

Also, when a part of the liquid-absorbent sheet is composed of aliquid-impermeable film and the the liquid-impermeable film portion isbrought into contact with food, as described, in JP-B-5-83214, theliquid-absorbent sheet cannot absorb the drip oozing from the food atthe contct surfaces, in particular, in the case that the liquidimpermeable film is disposed at hollow portions of the food or under thebottom portions of the food. The food is kept contacted with the dripfor a prolonged time and thus the absorption of drip cannot be attainedsufficiently.

SUMMARY OF THE INVENTION

The present invention has been made for solving the foregoing problemsand thus, the first object of the present invention is to provide aliquid-absorbent sheet which absorbs the drip oozing from food such asmeat and fish, and the drip staying at the bottom portions and thehollow portions of the food in contact with the liquid-absorbent sheetbut not positively absorbing water from the food, whereby the fooditself is not dried and discloration and deterioration in qualities ofthe food can be prevented for a prolonged time, so that a good yield canbe attained. The second object of the present invention is to provide amethod for storing a drippy food using the liquid-absorbent sheet.

The first object can be attained by providing a liquid-absorbent sheethaving included therein a liquid-absorbent material for absorbing dripsoozing from foods, wherein a part of the outer face of theliquid-absorbent sheet comprises a liquid-permeable film, at leastanother part of the outer face thereof comprises a liquid-semipermeablefilm, and the liquid-semipermeable film is a perforatedliquid-impermeable film having pores of a diameter falling within arange of from 0.05 mm to 0.5 mm, and a porosity falling within a rangeof from 0.01% to 0.4%.

The second object can be attained by a method for storing a drippy food,which camprises contacting the food with the liquid-semipermeable filmof the liquid-absorbent sheet and storing the food by vacuum packagingthe food with a gas impermeable film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a liquid-absorbent sheet of the presentinvention, and

FIG. 2 is a sectional view of another liquid-absorbent sheet of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The liquid-semipermeable sheet used in the liquid-absorbent sheet of thepresent invention is not a liquid-impermeable sheet permeating no waterbut is a sheet permeating a small amount of water in a restrained state,and it is practically a liquid-impermeable film as a packaging film forfoods but having provided therein pores defined according to the presentinvention.

Examples of the liquid-impermeable film include a polyethylene film, apolypropylene film, a polyvinylidene chloride film, a polyethyleneterephthalate (PET) film, a humidity-proofing cellophane, and apolyethylene-laminated aluminum foil. Of these films, a polyethylenefilm and a polypropylene film are particularly preferred since thesefilms do not contain or generate substances which may contaminate foods,do not have a water-absorbing property and a water permeability bythemselves, are flexible, have a good releasing property from the foodsto which the film is press-stuck, and also are inexpensive.

The liquid semipermeable film as used in the present invention isproduced by perforating a liquid-impermeable film such that the diameterd of the pores of the liquid-semipermeable film is in the range of from0.05 mm to 0.5 mm, and preferably from 0.1 mm to 0.3 mm and the porosityP thereof is in the range of from 0.01% to 0.4%, and preferably from0.01% to 0.2%. It is preferred that the pores are uniformly distributedover the whole liquid-semipermeable film. Also, there is no restrictionon the form of the pores if the diameter and the porosity are in theranges described above.

The porosity is the % value shown by A/B×100, wherein A is the totalarea of the pores and B is the whole area (including the areas of thepores) of the liquid-semipermeable film, and when the area j of eachpore is the same, the porosity is shown by (s×n×100)/B, wherein n is thenumber of the pores.

It is preferred that the food is brought into contact with the surfaceof the liquid-semipermeable film of the liquid-absorbent sheet and thefood is preserved by vacuum packaging with a gas-impermeable film. Thepores are for introducing the drip oozing from the food in contact withthe liquid-semipermeable film into the inside of the liquid-absorbentsheet through the pores, and for the purpose the diameter d of the poresis effective in the range of from 0.05 mm to 0.5 mm.

As the result of experiments, it has been found that when the diameter dof the pores is less than 0.05 mm, the drip oozing from the food remainon the liquid-semipermeable film without being passed through the pores.When the drip is allowed to be in contact with a food such as meat for along time, the contact surface of the meat is discolored into black.Also, when the diameter of the pores is over 0.5 mm, the drip and waterin the meat are absorbed by the liquid-absorbent sheet and blackeningwhich is considered to be the concentration of pigments occurs only atthe portions in contact with the pore portions of theliquid-semipermeable film to thereby cause spots on the surface of themeat. On the other hand, the porosity is too large, the interval betweeneach pores is narrowed, so that water and pigments of the meats arewholly absorbed by the liquid-absorbent sheet, and the meat is whollythinned. Thus, both the cases are inconvenient.

When the diameter of the pores becomes large, occurrence ofdiscoloration at the portions of the pores becomes significant. Further,it is difficult to uniformly provide the pores having a large diameterin production of the liquid semipermeable film. For the reasons, theoptimum diameter d of the pores, which absorb quickly the drips oozingfrom meat during the storage and which do not absorb water in meat, isin the range of from 0.1 mm to 0.3 mm.

It has been found that the porosity E is effective in the range of from0.01% to 0.4%. If the porosity p is less than 0.01%, the intervals amongthe pores becomes large and hence the drip is not effectively absorbedin the liquid-abosorption sheet through the pores, so that the drip isallowed to be in contact with the food such as meat for a long time toblacken the surface of meat. When the diameter of the pores becomeslarger, water in the meat at the peripheral portions of the pores isabsorbed through the pores and blackening, which is considered to be dueto concentration of pigments, occurs only at the portions to cause spotson the surface of meat.

Also, if the porosity P is over 0.4%, the intervals among the poresbecome narrow, whereby not only the drip but also water in the inside ofmeat are absrobed to thin the meat. The increase of the porosity meansthat the area of the pores becomes large and the absorbed amount ofwater with the liquid-absorbent sheet is increased. Thus, in view ofincreasing the yield, the optimum porosity P is in the range of from0.01% to 0.2%.

The liquid-semipermeable film can be produced by perforating theforegoing liquid-impermeable film by a known mechanicl or electric meansor with the use of laser, etc.

The liquid-permeable film as used in the present invention may bearbitrarily selected from generally available films which have a waterpermeability and water resistance, have such a density (pore size) as toprevent leakage of powdery polymeric water absorbent if used in theliquid-absorbent sheet, preferably have heat sealing properties and isacceptable for packaging foods. Examples of the liquid-permeable filminclude woven fabrics, knitted fabrics and nonwoven fabrics or laminatesthereof. A liquid-impermeable film (e.g., a polyethylene film, apolypropylene film, a PET film, or a moistureproof cellophane) in whichfine penetrating holes have been formed through the film by a knownmechanical or electrical means or with the use of laser, a foamedpolyethylene sheet having fine penetrating holes or a mesh sheet mayalso be used as the liquid-permeable film. In general, these films havea porosity of 1% or above and are thus clearly distinguishable from theabove-mentioned liquid-semipermeable film. The liquid-permeable filmpreferably has a porosity of about 10%. The liquid-permeable filmpreferably has a thickness of from 0.02 mm to 0.05 mm.

The liquid-permeable film is used for quickly permeating and absorbingdrips which ooze from the surface of food not in contact with theliquid-absorbent sheet and flow to the water absorption sheet bygravity, and shake during transporting of the food.

It is preferred that the liquid-semipermeable film and theliquid-permeable film have a heat-sealing property and each filmconstitutes each surface of the liquid-absorbent sheet of thisinvention.

By heat-sealing the peripheral portions of both the films, the peelingof the layers of the liquid-absorbent sheet can be prevented and alsoleakage of a liquid-absorbing material contained in the liquid-absorbentsheet can be prevented.

The liquid-absorbing material is used for absorbing and keeping thereinthe drips oozing from food, and any liquid-absorbing materials which donot give adverse inlfuences on the human bodies can be used in thepresent invention.

A polymeric water absorbent may be contained in the liquid-absorbentmaterial and may be arbitrarily selected from known materials which arecapable of absorbing drips and has a satisfactory safety. A number ofmaterials which generally have a three-dimensionaly crosslinkedstructure are known as a polymeric water absorbent. Preferable examplesinclude crosslinked products of polymers prepared by graft polymerizinga polysaccharide (e.g., starch or cellulose) with one or more substancesselected from the group consisting of acrylic acid, methacrylic acid,acrylic acid salts, methacrylic acid salts, acrylic acid esters,methacrylic acid esters, acrylamides, methacrylamides, acrylonitrile,methacrylonitrile, maleic acid, sulfonated styrene, polyvinyl pyridine,and oligomers or cooligomers thereof, optionally followed by hydrolysis;crosslinked products of one or more substances selected from the groupconsisting of polyethylene oxide, polypropylene oxide, polyvinylpyrrolidone, sulfonated polyethylene, polyvinyl pyridine, polyacrylicacid salts, polymethacrylic acid salts, polyacrylamide andpolymethacrylamide; vinyl acetate/acrylic acid salt copolymer;isobutylene/maleic anhydride copolymer; polyvinyl alcohol/maleic acidcopolymer; and crosslinked carboxymethylcellulose. Examples ofcommercially available polymeric water absorbents include PX-402A (aproduct of Showa Denko K.K.), Sunwet IM-300 (a product of Sanyo ChemicalIndustries, Ltd.), Aquakeep 10SH (a product of Seitetsu Kagaku KogyoK.K.) and Aqualic CA (a product of Nippon Shokubai Kagaku Kogyo Co.,Ltd.) may be cited.

It is preferred that the foregoing liquid-absorbing material is composedof the foregoing polymeric water absorbent sandwiched in capillaryliquid-absorbing materials capable of absorbing a liquid by acapillarity.

The capillary liquid-absorbing material is a sheet-form materialabsorbing drips or water by a capillarity and can keep them therein andpreferably contains the foregoing polymeric water absorbent. Morepreferably, the capillary liquid-absorbing material furhter contains awetting agent as will be described later. As examples of the capillaryliquid-absorbing material, there are a paper, a pulp, a pulp-formingsheet, an absorbent cotton, a gauze, a fabric, a knitted cloth, anonwoven fabric, a sponge, continuous cell type polyurethane foam, acontinuous cell type viscose foam, and a continuous cell type vinylonfoam. A preferred thickness of the liquid-absorbent material variesdepending upon the kind of the liquid-absorbent material. For example,the thickness is generally from about 0.03 mm to about 0.1 mm when gauzeor nonwoven fabric is used, and it is generally from about 1 mm to about10 mm when pulp, absorbent wadding or sponze is used. An absorbentwadding of 10 mm in thickness is preferably used for the purpose.

The polymeric water absorbent is generally a powder or a granular formin a dried state and thus for incorporating the polymeric waterabsorbent in the liquid-absorbent sheet, the polymeric water absorbentmay be scattered in a layer formed between two layers of the capillaryliquid-absorbing material and is kept between the two layers or may beinserted and kept in the insides of the continuous cells of thecapillary liquid-absorbing material constituting one layer. Also, acommercially available product keeping a polymeric water absorbent inthe capillary liquid-absorbing material, such as, for example, a paperdiaper, a sanitary napkin, and a high water absorbing sheet which isused in the fields of soil improving agents, etc., can be used as theliquid-absorbing material.

The polymeric water absorbent non-reversibly absorbs a large amount ofdrips and water introduced through the pores of the liquid-semipermeablefilm and the fine continuous holes of the liquid-permeable film, andfurther passed through the layer of the capillary liquid-absorbingmaterial, and does not flow backward even when a pressure or an impactis applied thereto.

It is preferred that the liquid-absorbing material of the presentinvention contains a wetting agent. In general, a polymeric waterabsorbent is hard in a dried state and hence in the case of such apolymeric water absorbent, there is a possibility of damaging theexterior packaging film and the gas-impermeable film for vacuumpackaging by friction, etc. On the other hand, since a wetting agentkeeps the softness even in the dried state, the occurrence of suchdamaging is prevented and, for example, the pinholing ratio of thegas-impermeable film can be lowered. Also, when the foregoing capillaryliquid-absorbing material has a hydrophobic surface, the initial waterabsorption is generally not sufficient. However, when in this case, thehydrophobic surface is covered by a wetting agent, the initial waterabsorption is improved and the drips and water introduced from the poresof the liquid-semipermeable film and the fine continuous holes of theliquid-permeable film can be quickly absorbed.

The amount of the wetting agent to be used is not particularly limited,as long as it can make the liquid-absorbent material flexible withoutundergoing leakage even under elevated pressure. The optimum amount ofthe wetting agent can be experimentally determined by taking account ofthe kind, constitution and total capillary wall area of the employedliquid-absorbent material.

Examples of the wetting agent include polyhydric alcohols such asethylene glycol, propylene glycol, diethylene glycol monoethyl ether,1,3-butylene glycol and glycerol; polyhydric alcohol polymers such aspolyethylene glycol, polypropylene glycol and polyglycerol; sugaralcohols such as xylitol, sorbitol and maltitol; and methylcellulose andcarboxymethylcellulose. If necessary, these wetting agents may be usedin the form of an aqueous solution. Among all, glycerol is particularlypreferable from the viewpoints of wetting ability and safety.

When the liquid-absorbent sheet of the present invention is brought intocontact with a food such that the surface of the liquid-semipermeablefilm is in contact with the food, and the food is vaccum packaged with agas-impermeable film to store, the drip oozing from portions of thefood, which are not in contact with the liquid-absorbent sheet, movethrough the gap between the foods and the gas impermeable film bygravity or upon being shaken during transport. Thus the drip is adsorbedoff with the liquid absorbing material of the liquid-absorbent sheetthrough the surface of the liquid-permeable film of the liquid-absorbentsheet disposed at the bottom or at the bottom and upper portions of ofthe food. Also, the drip oozing from the surfaces of the food in contactwith the liquid-absorbent sheet is absorbed by the liquid-absorbentsheet through the pores of the liquid-semipermeable sheet surface.

Furthermore, when hollow portions of the food wherein the drip is liableto stay is contacted with the liquid-absorbent sheet, the drip oozingfrom the food is absorbed by the liquid-absorbent sheet through thepores of the liquid-semipermeable film surface, whereby the food is notbrought into contact with the drip for a long time.

On the other hand, when the surface of the liquid-semipermeable filmhaving the pores of the diameter and the porosity described above is incontact with the food, water in the food is not positively absorbed bythe liquid-absorbing material, whereby the deterioration in quality anddiscoloration of the food due to drying do not occur.

When the liquid-absorbing material included in the liquid-absorbentsheet contains the polymeric water absorbent, the drip once absorbed isnot released to the food side even when applied to the liquid absorbingmaterial a pressure or an impact during the storage or thetransportation of foods.

When the liquid-absorbing material contains a wetting agent, theliquid-absorbing material is softened and the pinholing ratio of thegas-impermeable film used for vacuum packaging is lowered.

Then, the present invention is explained by referring to the accompanieddrawings.

FIG. 1 shows a preferred example of the liquid-absorbent sheet of thepresent invention.

In the practical example shown in FIG. 1, a liquid-absorbent sheet 1contains a liquid-absorbing material 4 for absorbing drips of food, oneof the external surfaces of the liquid-absorbing material 4 is composedof a liquid-permeable film 5, and the other external surface is composedof a liquid-semipermeable film 6. The liquid-semipermeable film 6 iscomposed of a liquid-impermeable film such as, preferably, apolyethylene film or a polypropylene film, having formed therein pores,and the pores have the specific diameter and the specific porosity asdescribed above.

It is preferred that the liquid-absorbing material 4 is formed in asheet form by sandwiching a sheet-form polymeric water absorbent 2 withcapillary liquid-absorbing materials 3 and 3' as shown in FIG. 2 andfurther it is preferred that the liquid-absorbing material 4 contains awetting agent.

It is also preferred that the liquid-semipermeable film 6 and theliquid-permeable film 5 have a heat-sealing peroperty and both the filmsare heat-sealed at the peripheral portions.

For preserving a drippy food such as meat, fish, fish meat, etc., usingthe liquid-absorbent sheet 1 of the present invention, the food isplaced on the liquid-absorbent sheet 1 in the state that the food isbrought into contact with the liquid-semipermeable film 6 and at least apart of the liquid-absorbent sheet is disposed at the bottoms of thefood during transportation or preservation of the food and the food isvacuum packaged with a gas-impermeable film.

In this case, the gas-impermeable film used may be an ordinarygas-impermeable film, a shrunk film, etc., generally used for vacuumpackaging of food. Also, in this case, the vacuum degree may be such anextent that the food is closely contacted with the liquid-absorbentsheet 1 and the gas-impermeable film.

During the sotrage of food such as, for example, frozen meants, partialmeats, etc., of beef, pork, chiken, etc., and fish meats such as tunas,bonitos, salmon, etc., drips oozing from the food are absorbed in theinside of the liquid-absorbent sheet 1 through the pores 7 of theliquid-semipermeable film 6, and are spontaneously retained in thecapillary liquid-absorbing material 3 and also non-reversibly absorbedand kept in the polymeric water absorbent 2.

The drips oozing from the surface of the food not in contact with theliquid-absorbent sheet 1 go around the back side of the liquid-absorbentsheet 1 and quickly absorbed from the liquid-permeable film 5, wherebythe drips do not remain on the surfaces of the food. Also, the dripsoozing from the surfaces of the food in contact with theliquid-semipermeable film 6 are absorbed in the inside of theliquid-absorbent sheet 1 through the pores 7 of the liquid-semipermeablefilm 6. Thus, when the liquid-absorbent sheet 1 is in contact with thesurfaces of the food, the drips do not stay in hollow portions of thefood.

Then, practical examples of the liquid-absorbent sheet of the presentinvention and examples for confirming the effects thereof are shownbelow.

EXAMPLE 1

A liquid-absorbent sheet of the structure as shown in FIG. 1 wasprepared. Namely, a pulp sheet having a thickness 10 mm and weighing 400g/m² was employed as liquid-absorbent material 4 and a nonwovenpolypropylene fabric was laminated as liquid-permeable film 5 onto oneface of the pulp liquid-absorbent material. Onto another face of thepulp liquid-absorbent material, was laminated a polyethylene film(TUX-HC30, a product of Tokyo Cellophane K.K.), in which circular pores7 had been formed at a diameter of 0.04 mm to 1.0 mm and at a porosityof 0.008% to 0.60%, as liquid-semipermeable film 6, to thereby give aliquid-absorbent sheet.

The liquid-semipermeable film face of this liquid-absorbent sheet wasbrought into contact with meat samples (sirloin (about 7 kg) and roundbeef (about 10 kg) of a Japanese Holstein; sirloin (about 5 kg) of aJapanese pig), vacuum packaged with a gas-impermeable film and thencold-stored for 10 days. Then the package was opened and the conditionsof the stored meat samples were evaluated. Pigments in the food movealong with water in the food, and thus the movement of water can bemonitored by way of obserbing dolor of the food. The results obtainedare shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Poro-                                                                         sity                                                                              Pore Diameter (mm)                                                        (%) 0.04                                                                             0.05                                                                              0.1                                                                              0.2 0.3                                                                              0.4 0.5                                                                              0.6 0.7                                                                              1.00                                       __________________________________________________________________________    0.008                                                                             x Δ                                                                        x Δ                                                                         x Δ                                                                        x Δ                                                                         x Δ                                                                        x Δ                                                                         x Δ                                                                        x * x *                                                                              x *                                        0.01                                                                              x Δ                                                                        ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       x * x *                                                                              x *                                        0.02                                                                              x Δ                                                                        ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ *                                                                   x *                                                                              x *                                        0.05                                                                              x Δ                                                                        ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ *                                                                   ∘ *                                                                  x *                                        0.10                                                                              x Δ                                                                        ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ *                                                                   ∘ *                                                                  x *                                        0.20                                                                              -- ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ *                                                                   ∘ *                                                                  ∘ *                            0.30                                                                              -- --  ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ *                                                                   ∘ *                                                                  ∘ *                            0.40                                                                              -- --  -- ∘ □                                                        ∘ □                                                       ∘ □                                                        ∘ □                                                       ∘ ▪                                                         ∘ *                                                                  ∘ *                            0.50                                                                              -- --  -- ∘ ▪                                                         ∘ ▪                                                        ∘ ▪                                                         ∘ ▪                                                        ∘ ▪                                                         ∘ ▪                                                        ∘ *                            0.60                                                                              -- --  -- ∘ ▪                                                         ∘ ▪                                                        ∘ ▪                                                         ∘ ▪                                                        ∘ ▪                                                         ∘ ▪                                                        ∘ *                            __________________________________________________________________________     Criteria for evaluation                                                       ∘: No drip on the surface of the meat.                            x: Drips exist on the surface of the meat.                                    □: The color of the meat is same as that of the surface not in     contact with the liquidabsorbent sheet.                                       ▪: The color of the meat is clearly faint as compared with that     of the surface not in contact with the sheet.                                 Δ: The color of the meat is clearly blackened as compared with the      portion in contact with the sheet.                                            *: The portions of the meat in contact with the pores are clearly             blackened as compared with the surface not in contact with the sheet.    

As shown in the results in Table 1, when the pore diameter is not largerthan 0.04 mm, since the drips at the contact surface of theliquid-absorbent sheet and the surface of the meat cannot be absorbedinto the liquid-absorbent sheet through the pores, the drips remainbetween the liquid-absorbent sheet and the meat, whereby the surface ofthe meat is blackened. Also, when the pore diameter is 0.60 mm orlarger, the diameter of the pores is too large and hence water in theportions of the meat in contact with the pore portions are adsorbed bythe liquid-absorbent sheet together with the drips to cause theconcentration of pigments at the portions in contact with the pores,whereby the surface of the meat is spot-like discolored.

In this case, however, when the porosity is increased, the intervalsamong the pores are narrowed and hence drips and water are absorbed bythe liquid-absorbent sheet from the whole surface of the meat in contactwith the liquid-absorbent sheet, whereby the color of the surface of themeat becomes wholly faint.

When the porosity becomes lower than 0.008%, since the intervals amongthe pores are broadened, the drips cannot be introduced into theliquid-absorbent sheet through the pores, whereby the drips remain andare in contact with the meat for a long time and thus the meat isblackened. In this case, however, when the size of the pores becomeslarge, at the pores and at the peripheral portions of the pores, thedrips and water are locally absorbed by the liquid-absorbent sheet,whereby the surface of the meat at the pore is blackened caused by theconcentration of pigments to form black spots on the meat surface.

Also, when the porosity becomes higher than 0.5%, the intervals amongthe pores are narrowed, much water in the food is absorbed by theliquid-absorbent sheet together with the drips and also pigments in themeat are transferred together with water in the meat, whereby the colorof the meat becomes faint. However, when the diameter of the pores islarge, the local absorption is strong, which causes the concentration ofpigments in the meat, whereby the surface of the meat is spot-likeblackened at the portions of the pores.

Thus, it has been confirmed that since in the case of using theliquid-absorbent sheet sample wherein the diameter of the pores is inthe range of from 0.05 mm to 0.5 mm and the porosity thereof is in therange of from 0.01% to 0.4%, the drips are not remained on the surfaceof the food and also the food is not discolored, water is nottransferred from the food to the liquid-absorbent sheet in this case.

EXAMPLE 2

Three liquid-absorbent sheet samples, which were referred torespectively as liquid-absorbent sheets A, B and C, were prepared.

Liquid-absorbent sheet sample A: A liquid-absorbent sheet having astructure as shown in FIG. 1 wherein liquid-semipermeable film 6 havinga diameter of the pores of 0.2 mm and a porosity of 0.1% was used.

Liquid-absorbent sheet sample B: A liquid-absorbent sheet having astructure as shown in FIG. 1 wherein the liquid-semipermeable film wasreplaced by an unperforated liquid-impermeable film (TUX-HC30, a productof Tokyo Cellophane).

Liquid-absorbent sheet sample C: A liquid-absorbent sheet having astructure as shown in FIG. 1 wherein the liquid-semipermeable film wasreplaced by a nonwoven polypropylene fabric similar to theliquid-permeable film.

Food sample: The sirloin (about 7 kg) of a Japanese Holstein.

Storage test: The food samples were brought into contact with theliquid-semipermeable film face, the liquid-impermeable film face and theliquid-permeable film face of the liquid-absorbent sheet samples A, Band C, respectively, and then vacuum packaged. After cold-storing for10-days, each package was opened and the color change in the meat sampleand the presence of drips oozing from the food sample onto the contactface were observed. The results obtained are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Sheet sample  Conditions of meat                                                                           Dripping                                         ______________________________________                                        A:    semipermeable                                                                             No color change both                                                                         No drip.                                           film        in surface and inside.                                      B:    impermeable Color change in part                                                                         Drips on part in                                   film        in contact with the                                                                          contact with the                                               sheet, but no color                                                                          sheet.                                                         change in inside.                                           C:    double face Discoloration in part                                                                        No drip.                                           permeable film                                                                            in contact with the                                                           sheet, discoloration                                                          and dryness in inside.                                      ______________________________________                                    

It is seen from in Table 2, that when the liquid-absorbent sheet sampleA, i.e., an example of the liquid-absorbent sheet according to thepresent invention, was used, the food could be stored while being freefrom any discoloration/color change, dryness or dripping.

In contrast, when liquid-absorbent sheet sample B having theliquid-impermeable film in the part to be in contact with the food wasused, a large amount of dripps were pooled in the hollow on the surfaceof the food being in contact with the sheet and also a color change wasobserved in this part. When liquid-absorbent sheet sample C having aliquid-permeable film in the part to be in contact with the food wasused, on the other hand, discoloration/color change occurred in the meatnot only at the part being in contact with the liquid-absorbent sheetbut also in the inside of the food. In this case, further, the meat wasslightly dried, which made it commercially unacceptable.

EXAMPLE 3

Four kinds of liquid-absorbent sheet samples D, E, F, and G wereprepared. The size of each liquid-absorbent sheet sample was 10 cm×12cm.

Liquid-absorbent sheet samples: Each sample was the liquid-absorbentsheet having the structure shown in FIG. 2. Pulp sheets each having athickness of 1.0 mm and a basis weight of 40 g/m² was used as thecapillary liquid-absorbing materials 3 and 3', and a polyacrylic acidseries high water absorbing polymer (Aquaric CA, trade name, made byNippon Shokubai Kagaku Kogyo Co., Ltd.) was uniformly scattered as thepolymeric water absorbent 2 between the capillary liquid-absorbingmaterials 3 and 3', and sandwiched in the materials in a sheet form toprovide a liquid-absorbing material 4.

As shown in Table 3, in the liquid-absorbent sheet sample D, aliquid-semipermeable film having pores 7 each having a diameter of 0.2mm and having a porosity of 0.04% was used as the liquid-semipermeablefilm 6 and also a liquid-impermeable film (TUX-HC30, trade name, made byTokyo Cellophane K.K.) without having pores was used in place of theliquid-permeable film 5. In the liquid-absorbent sheet sample E, aliquid-semipermeable sheet having pores 7 each having a diameter of 0.2mm and a porosity of 0.04% was used as the liquid-semipermeable sheet 6and a polypropylene-made nonwoven fabric was used as theliquid-permeable film 5. In the liquid-absorbent sheet sample F, aliquid-impermeable film having no pores was used in place of theliquid-semipermeable film 6 and a polypropylene-made nonwoven fabric wasused as the liquid-permeable film 5. In the liquid-absortion sheetsample G, a polypropylene-made nonwoven fabric was used as aliquid-permeable film in place of the liquid-semipermeable film 6 and aliquid-impermeable film having no pores was used in place of theliquid-permeable film 5.

Food sample: Domestic beef (Holstein-Friesian), portion; sirloin (about7 kg).

Storage test: The same food sample was brought into contact with thesurface of the film of each liquid-absorbent sheet sample, the filmbeing shown in Table 3 as the film for contact with food, they arevaccum packaged with a gas-impermeable film, after cold-storing thepackaged food for 10 days, the package was opened, and the amount ofdrips absorbed by each liquid-absorbent sheet sample was measured andthe presence of the drips on the contact surface of eachliquid-absoption sheet sample and the meat was observed.

The test results are shown in Table 4 below.

                  TABLE 3                                                         ______________________________________                                        Liquid-absorbent                                                                           Film used for con-                                                                          Film used for non-                                 Sample       tact with meat                                                                              content with meat                                  ______________________________________                                        D            Liquid-semiperme-                                                                           Liquid-impermeable                                              able film     film                                               E            Liquid-semiperme-                                                                           Liquid-permeable                                                able film     film                                               F            Liquid-impermeable                                                                          Liquid-permeable                                                film          film                                               G            Liquid-permeable                                                                            Liquid-impermeable                                              film          film                                               ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                                  Presence of drip                                                              at contact surface                                  Liquid-absorbent                                                                           Absorbed amount of                                                                         between the sheet                                   sheet sample drip (g)     and the meat                                        ______________________________________                                        D            8            none                                                E            38           none                                                F            32           found                                               G            42           none                                                ______________________________________                                    

From the results shown in Table 4, it can be seen that by comparing theabsorbed amunts of the drip between the liquid-absorbent sheet samples Dand G, the absorbed amount of drip in the sample D is about 20% of theabsorbed amount of the drip in the sample G which shows theliquid-absorbing property as the liquid-semipermeable film. It is alsoseen from the comparison of the absorbed amounts of the drip between theliquid-absorbent sheet samples E and F, the absorbed amount of the dripin the sample E using the liquid-semipermeable film is about 20% largerthan that in the sample F. The drip at the contact surface of the meatand the liquid-absorbent sheet is not obserbed in the sample E, but itis abserved in the sample F. Thus, the function of theliquid-semipermeable film is confirmed.

EXAMPLE 4

The liquid-absorbent sheet having the construction shown in FIG. 1 wasprepared.

That is, as the liquid-absorbing material 4, a pulp sheet having athickness of 10 mm and a basis weight of 400 g/m² was used and on onesurface thereof was laminated a polypropylene-made nonwoven fabric asthe liquid-permeable film. Also, on another surface of theliquid-absorbing material 4 was laminated a polyethylene film (TUX-HC30,trade name, made by Tokyo Cellophane K.K.) having formed thereincircular pores 7 having a diameter of 0.2 mm and a porosity of 0.1% asthe liquid-semipermeable film to provide a liquid-absorbent sheet.

The surface of the liquid-semipermeable film 6 of the liquid-absorbentsheet was brought into contact with each of meats (domestic beef(Holstein-Friesian), portion; sirloin (about 7 kg), round (about 10 kg):domestic pork, portion; sirloin (about 5 kg)!, the meat was vacuumpackaged in the contacted state, after cold-storing the packaged meatfor 10 days, the package was opened, and the state of the meat wasobserved.

As a result, discoloring of each meat was not observed, and no drip wasobserved at the contact portion of the meat with the liquid-absorbentsheet.

COMPARATIVE EXAMPLES 1 AND 2

By following the same procedure as in Example 4 except that aliquid-semipermeable film having circular pores 7 having a diameter of0.01 mm and the porosity of 0.01% was used as the liquid-semipermeablefilm, the liquid-absorbent sheet of Comaprative Example 1 was prepared.

By following the same procedure as in Example 4 except that aliquid-semipermeable film having circular pores 7 having a diameter of1.0 mm and the porosity of 1.0% was used as the liquid-semipermeablefilm, the liquid-absorbent sheet of Comparative Example 2 was prepared.

Using each of the samples prepared in Comparative Examples 1 and 2, themeats were cold-reserved as in Example 4 and then the states of themeats were observed.

In the case of using the sample obtained in Comaprative Example 1,discoloration was observed at the contact portion of each meat and withthe liquid-absorbent sheet and also a large amount of drips remained atthe portion.

In the case of using the sample obtained in Comparative Example 2, dripswere not observed but spot-like discoloration corresponding to the poreswas observed at the contact portion of each meat with theliquid-absorbent sheet.

EXAMPLE 5

The liquid-absorbent sheet having the construction shown in FIG. 2 wasprepared.

That is, pulp sheets each having a thickness of 1.0 mm and a basisweight of 40 g/m² were used as the capillary liquid-absorbing materials3 and 3', and a polyacrylic acid series high water absorbing polymer(Aquaric CA, trade name, made by Nippon Shokubai Kakagu Kogyo Co., Ltd.)was uniformly scattered between these sheets and sandwiched in a sheetform to provide a liquid-absorbing material 4.

On one surface of the liquid-absorbing material 4 was laminated apolypropylene-made nonwoven fabric as the liquid-permeable film 5. Also,on the other surface of the liquid-absorbing material 4 was laminated apolyethylene film (TUX-HC30, trade name, made by Tokyo Cellophane K.K.)having formed therein circular pores 7 having a diameter of 0.2 mm andthe porosity of 0.1% as the liquid-semipermeable film 6 to provide aliquid-absorbent sheet.

The surface of the liquid-semipermeable film of the liquid-absorbentsheet 1 was brought into contact with a meat domestic beef(Holstein-Friesian), portion; sirloin (about 7 kg)!, and meat was vacuumpackaged with a gas-impermeable film (Battier Back, trade name, made byGrace Co.) in the contact state, after cold-storing the packaged meatfor 10 days, the package was opened and the state of the meat wasobserved.

In this case, any discoloration was not observed on the meat. Also,drips were not observed at the contact portion of the meat with theliquid-absorbent sheet.

After the foregoing test, the liquid-absorbent sheet 1 was took out andwhen a pressure of 10 kg/cm² was applied thereon, the flow out of dripswas not observed. From the result, it can be seen that the use of thepolymeric water absorbing material as the liquid-absorbing material iseffective for preventing flowing backward of the drips.

EXAMPLE 6

The liquid-absorbent sheet having the construction shown in FIG. 2 wasprepared.

That is, thin virgin pulp sheets each having a thickness of 1.0 mm and abasis weight of 40 g/m² were used as the capillary liquid-absorbingmaterials 3 and 3', and a polyacrylic acid series high water absorbingpolymer (Aquaric CA, trade name, made by Nippon Shokubai Kagaku KogyoCo., Ltd.) was uniformly scattered between the sheets as the polymericwater absorbent 2 and sandwiched in a sheet form to provide aliquid-absorbing material 4.

The liquid-absorbing material 4 was impregnated with 10% by weight foodadditive glycerol as a wetting agent.

On one surface of the liquid-absorbing material 4 containing the wettingagent was laminated a polypropylene-made nonwoven fabric as theliquid-semipermeable film 6, and on the other surface of theliquid-absorbing material 4 was laminated a polyethylene film (TUX-HC30,trade name, made by Tokyo Cellophane K.K.) having therein pores 7 havinga diameter of 0.2 mm and the porosity of 0.1% to provide aliquid-absorbent sheet 1.

The surface of the liquid-semipermeable film 6 of the liquid-absorbentsheet 1 was brought into contact with a meat domestic beef(Holstein-Friesian), portion; sirloin (about 7 kg)!, the meat was vacuumpackaged with a gas-impermeable film (Barrier Back, trade name, made byGrace Co.) in the contacted state, and thus 100 packaged samples wereprepared. After cold-storing the packaged samples for 10 days, theforming ratio of pinholes in each gas-impermeable film used for thepackage was measured. The pinhole forming ratio relates to the vacuumduring the preservation and is an important factor for keeping foodsfreshness.

As a results of the measurement, the pinhole forming ratio was 0%. Forcomparison, when the same test as above was carried out without usingthe wetting agent, the pinhole forming ratio was 3%. It can be seen thatthe use of a wetting agent is effective for reducing the pinhole formingratio of a packaging material.

Since the liquid-absorbent sheet of the present invention contains aliquid-absorbing material and has on the outer surface aliquid-semipermeable film having formed therein pores having a diameterof from 0.05 mm to 0.5 mm and the porosity of from 0.01% to 0.4%, whenfood is stored in contact with the surface of the liquid-semipermeablefilm, drips oozing from food such as meat, fish, etc., are absorbed wellto prevent the contact surfaces of the food from being discolored anddenatured, and since the liquid-absorbent sheet does not absorb water inthe food, so that the reduction of weight of the food by drying andlowering of the commercial value of the food is prevented.

Also, since the other surface of the liquid-absorbent sheet is composedof a liquid-permeable film, a large amount of drips and water at thawingare quickly absorbed from the surface, whereby the occurrence ofdenaturing of food is prevented.

When the liquid-absorbing material contains a polymeric water absorbent,since the polymeric water absorbent quickly absorbs a large amount ofdrips and non-reversibly keeps the drips to an external pressure, thedrips are always smoothly absorbed during the storage and transportionof food and also the drips absorbed do not flow back to the food side.

When the liquid-absorbing material contains a wetting agent, since thewetting agent strengthens the suction force of the liquid-absorbingmaterial for drips and softens the liquid-absorbing material, thepinhole forming ratio of the packaging material is lowered and thefreshness of the food can be surely maintained.

The liquid-absorbent sheet of the present invention having theadvantages as described above can be effectively used for the storage ofdrippy foods, such as meat, fish, etc., and can not only keep thequality and the yield high in the case of vacuum packaging the food andtransporting or storing but also in the case of opening the package andcooking or selling by placing the food on a shop front, when theliquid-absorbent sheet is laid, the freshness keeping period of time orthe relishing time can be prolonged.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A method for storing foods, which comprises(i)providing a liquid-absorbent sheet containing a liquid-absorbingmaterial capable of absorbing drips of food, wherein a part of one outersurface of the liquid-absorbent sheet is composed of a liquid-permeablefilm, a part of the other outer surface thereof is composed of aliquid-semipermeable film, the liquid-semipermeable film is aliquid-impermeable film having formed therein pores, the diameter ofeach of the pores is in the range of from 0.05 mm to 0.5 mm, and theporosity of the pores is in the range of from 0.01% to 0.4%, (ii)contacting the food with the surface of the liquid-semipermeable film ofthe liquid-absorbent sheet, and (iii) vacuum packaging the food and theliquid-absorbent sheet together using a gas-impermeable film.
 2. Amethod for storing foods as in claim 1, wherein the diameter of thepores of the liquid-semipermeable film formed is in the range of from0.1 mm to 0.3 mm and the porosity thereof is in the range of from 0.01%to 0.2%.
 3. A method for storing foods as in claim 1, wherein theliquid-semipermeable film is a polyethylene film or a polypropylene filmhaving formed therein pores.
 4. A method for storing foods as in claim1, wherein the liquid-absorbing material contains a polymeric waterabsorbent.
 5. A method for storing foods as in claim 1, wherein theliquid-absorbing material contains at least one wetting agent selectedfrom the group consisting of ethylene glycol, propylene glycol,diethylene glycol monoethyl ether, 1,3-butylene glycol, glycerol,polyethylene glycol, polypropylene glycol, polyglycerol, xylitol,sorbitol, maltitol, methyl cellulose, and carboxymethyl cellulose.
 6. Amethod for storing foods as in claim 1, wherein the liquid-absorbingmaterial has a polymeric water absorbent sandwiched in a sheet form withcapillary liquid absorbing materials, and contains a wetting agent, saidliquid-absorbing material is sandwiched between the liquid permeablefilm and the liquid semipermeable film, and both the films areheat-sealed at the peripheral portions thereof.